It looks like you're trying to bind the value of 'option.weightCoffee' to the 'select' element using 'formControl', the correct syntax for binding a form control to a select element is using the [formControl] directive. Your code should be -
<select class="form-control" [formControl]="selectedRoastingOption" id="weightCoffee" (change)="onRoastingoption($event.target.value)">
<option value="">please select roasting option ...</option>
<option *ngFor="let option of products.variants" [value]="option.weightCoffee">{{ option.weightCoffee }}</option>
</select>